1. Field of the Invention
The present invention relates to a strain compensation amplifier for use in a base station, a relay apparatus, and the like of mobile communication systems such as a car phone, a cellular phone, and a personal handy phone system, and relates to miniaturization, loss reduction and cost reduction achieved by unifying a part of a circuit.
2. Description of the Related Art
A base station and a radio relay apparatus in a car phone, a cellular phone system, and the like are provided with a multifrequency common amplifier for simultaneously amplifying a multifrequency signal. In the multifrequency common amplifier, linearity needs to be sufficiently improved in order to minimize occurrence of mutual modulation strain, and a small-size high-linearity amplifier has been used. As one of the amplifiers, a strain compensation amplifier (self-adjusting feedforward amplifier) is used, and constituted in such a manner that the mutual modulation strain and noise generated in the amplifier are compensated by self adjustment.
This strain compensation amplifier is constituted of a strain detection circuit and a strain removal circuit, the strain detection circuit including a main amplifier which is a compensation object amplifier detects a strain component except an input signal, the detected strain component (error component) is inputted to the strain removal circuit including an auxiliary amplifier (error amplifier) to amplify the strain component, and subsequently negative-phase synthesis with a multifrequency amplification signal is performed to offset the strain component in the constitution.
FIG. 5 is a diagram showing a constitution example of a conventional strain compensation amplifier. In FIG. 5, numeral 1 denotes an input terminal, 2 denotes a power distributor for distributing an output of the terminal, 3 denotes a first variable attenuator, 4 denotes a first variable phase unit, 5 denotes a main amplifier, 6 denotes a delay line, 7 denotes a first power synthesizer, 8 denotes a second variable attenuator, 9 denotes a second variable phase unit, 10 denotes an auxiliary amplifier, 11 denotes a delay filter, 12 denotes a second power synthesizer, 13 denotes a directional coupler, 14 denotes an isolator, 15, 16 denote terminating resistors, 17, 18, 19 denote coaxial cables, 20 denotes an output terminal, 21 denotes a monitor terminal, and 22 denotes a connector.
An input signal Pin is inputted to the power distributor 2 from the input terminal 1, passed through two branched main lines, and distributed to the delay line 6 and first variable attenuator 3, and an output of the first variable attenuator 3 is passed through the first variable phase unit 4 and amplified by the main amplifier 5. An amplification signal including a strain component generated during amplification is inputted to the first power synthesizer 7, and synthesized with the input signal passed through the main line distributed by the power distributor 2 and the delay line 6 by the first power synthesizer 7, so that the strain component is detected.
The amplification signal outputted from the first power synthesizer 7 is inputted to the second power synthesizer 12 via the delay filter 11. On the other hand, the strain component outputted from the first power synthesizer 7 is passed through the second variable attenuator 8 and second variable phase unit 9, amplified by the auxiliary amplifier 10, inputted to the second power synthesizer 12 so that polarity is reversed, and synthesized with the amplification signal including the strain component inputted via the delay filter 11 so that the strain component is offset, and a common amplification signal with little strain is outputted. For this output, a monitor output is obtained from the monitor terminal 21 by the directional coupler 13, a unidirectional property is enhanced by the isolator 14, and an output signal Pout is outputted via the output terminal 20. Here, the delay filter 11 and second power synthesizer 12, the second power synthesizer 12 and directional coupler 13, and the directional coupler 13 and isolator 14 are connected to each other, respectively, via the connectors 22 and coaxial cables 17, 18, 19, and the terminating resistors 15, 16 are connected to the second power synthesizer 12 and the directional coupler 13 via the connectors. In this strain compensation amplifier, the variable attenuators 3, 8, and variable phase units 4, 9 are adjusted by a pilot signal control and a desired operation is performed. Additionally, these control systems are omitted from FIG. 5.
Moreover, in the conventional power synthesizer, and directional coupler, a tri-plate structure is generally used in which an electrode pattern is held between dielectric substrates in a sandwich manner as shown in FIG. 6. The electrode pattern is connected to an input/output terminal, and entirely contained in a shield case. The dielectric used in the tri-plate structure is slightly larger than air in loss. Furthermore, since the conventional power synthesizer and directional coupler are individually contained in the shield cases, a large number of assembly processes are necessary.
In the conventional strain compensation amplifier, the power distributor and delay unit of the strain detection circuit, and the delay unit, power synthesizer, directional coupler, isolator, and terminating resistor of the strain removal circuit are constituted separately from one another, contained separately in the individual shield cases, and coupled to one another by the connectors and coaxial cables. Additionally, since the delay filter or the delay line using the coaxial cable is used in the delay unit, it is difficult to miniaturize the strain compensation amplifier. For connection via the connector and coaxial cable, since an operation space is necessary during assembly, it is further difficult to miniaturize the amplifier. Furthermore, efficiency enhancement of the strain compensation amplifier, loss reduction particularly on and after the first power synthesizer, material cost reduction and assembly process number reduction and another cost reduction raise problems.
In order to miniaturize the strain compensation amplifier, miniaturization of the strain removal circuit needs to be performed, and to realize low power consumption, a necessity of reducing power loss in the strain removal circuit has occurred.
An object of the present invention is to solve the aforementioned problems, and provide a strain compensation amplifier which realizes miniaturization, loss reduction, and cost reduction.
To achieve the aforementioned object, in the strain compensation amplifier of the present invention, the following means is used to realize miniaturization, loss reduction, and cost reduction of the strain compensation amplifier.
Specifically, according to the present invention, there is provided a strain compensation amplifier including: a strain detection circuit in which an input signal is distributed by a power distributor, and a signal obtained by amplifying one output by a main amplifier via a first variable attenuator and a first variable phase unit is synthesized with a signal obtained by adjusting a timing of another output distributed from the power distributor by a first delay unit by a first power synthesizer to detect a strain component generated in the main amplifier; and a strain removal circuit in which a signal obtained by amplifying the strain component outputted from the first power synthesizer by an auxiliary amplifier via a second variable attenuator and a second variable phase unit is reverse-phase synthesized with a signal obtained by adjusting a timing of a signal outputted from the first power synthesizer and amplified by the main amplifier by a second delay unit by a second power synthesizer to offset the strain component, a monitor output is obtained by a directional coupler, and a unidirectional property is enhanced by an isolator to obtain a power synthesis output, and in this strain compensation amplifier, at least two or more of the power distributor, the first delay unit, the first power synthesizer, the second delay unit, the second power synthesizer, the directional coupler, the isolator, a terminating resistor of the second power synthesizer, and the terminating resistor of the directional coupler are unified.